Conventional methods for obtaining a zirconia sol include: a method for heat-hydrolyzing a zirconium salt aqueous solution, a method for adding hydrogen peroxide to a zirconium salt aqueous solution and heating the resultant solution, and a method for heating zirconium hydroxide in a basic region.
There is disclosed a method for hydrolyzing a reaction product between zirconium ammonium carbonate and a chelating agent (for example, oxyphenols, amino alcohols, oxyacids, polycarboxylic acids, oxyaldehydes, amino acids, and β-diketones) (see, Patent Document 1).
There is disclosed a production method of a basic zirconia sol including: maintaining an aqueous suspension containing zirconium hydroxide in a heated state at 80° C. or more until the crystallinity of produced zirconia becomes 80% or more to obtain an aqueous suspension containing crystallized zirconia; and adding to the obtained aqueous suspension, a basic compound containing nitrogen (primary amine, secondary amine, or quaternary ammonium hydroxide), a hydroxide of an alkali metal or alkaline earth metal (see, Patent Document 2).
There is disclosed a production method of a zirconia sol including: causing a precipitate by adding a base to a zirconium salt aqueous solution; adding thereto, a hydroxide of an alkaline earth metal or an aqueous solution thereof to obtain a suspension; and heat-aging the obtained suspension at a temperature of 90 to 200° C. (see, Patent Document 3).
There is disclosed a production method of a zirconia sol including: heating a zirconium salt aqueous solution having a molar ratio of anion/metal of 0.5/1 to 4/1 to 120 to 300° C. and cooling the heated solution to room temperature; and adjusting the pH value of the solution to 2 to 6 (see, Patent Document 4).
There is disclosed a production method of a zirconia sol including: adding hydrogen peroxide to a zirconium salt aqueous solution having a concentration of 0.05 to 2.0 mol/L in an amount which is about half the amount of zirconium in the aqueous solution or more in the molar ratio; heating the resultant solution to 80 to 300° C.; and adding to the solution further a base, such as ammonia, or treating the solution with an ion-exchange resin or the like (see, Patent Document 5).
There is disclosed a production method of zirconia-based fine particles including: heating to 80 to 250° C. and hydrolyzing a zirconium salt aqueous solution to form crystalline zirconia fine particles; separating by precipitation method a part of the thus-formed crystalline zirconia fine particles having a secondary aggregated particle diameter of approximately 1000 Å or more on average from another part of the thus-formed crystalline zirconia fine particles to produce a zirconia sol; and subjecting the produced zirconia sol individually or in combination with another metal compound to a thermal treatment at a temperature of 1000° C. or less (see, Patent Document 6).    Patent Document 1: Japanese Patent Application Publication No. JP-A-3-174325    Patent Document 2: Japanese Patent Application Publication No. JP-A-64-083519    Patent Document 3: Japanese Patent Application Publication No. JP-A-60-176920    Patent Document 4: U.S. Pat. No. 2,984,628 Specifications    Patent Document 5: Japanese Patent Application Publication No. JP-A-58-079818    Patent Document 6: Japanese Patent Application Publication No. JP-A-58-217430